This invention relates generally to the field of flue dampers for conducting the products of combustion in a furnace to the outside atmosphere. More particularly, it relates to an improved construction of this type of relatively simple design permitting correspondingly low cost of manufacture, and with high reliability in operation. Devices of this general type are well known in the art, and the invention lies in specific constructional details which permit these advantages.
In those installations having a gun type oil burner, it is common practice to provide a side vent which employs a counter balanced butterfly valve to establish periodic communication between the lower end of the flue and the furnace room. When this valve is open, air flows from the furnace room to the flue to maintain draft emanating from the oil burner at a relatively constant level during burner operation. However, when the burner is not in operation, a substantial wind passing the open end of the flue will also draw warm air from the furnace plenum and thereby waste fuel necessary to reheat the plenum when the burner commences a subsequent cycle of operation.
With the rapid increase in the cost of petroleum fuels, attempts have been made to provide a flue damper which will positively close the flue above the side vent to stop the flow of warm air up the flue when the burner cycle has ended. A common type includes a butterfly type valve operated by a motor or an electrical solenoid energized simultaneously with the oil burner motor. While effective, this construction is quite costly, and requires the efforts of both an electrician and a plumber to install.
Somewhat simpler structures are described in the United States patent to Sabins, U.S. Pat. No. 2,264,590 granted Dec. 2, 1941, and a series of patents granted to Steinen, namely U.S. Pat. Nos. 2,904,255 of Sept. 15, 1951; 2,990,118 granted June 27, 1961; 3,070,312 granted Dec. 25, 1962; and 3,077,305 granted Feb. 12, 1963. Each of the above patents teaches an in-line damper of butterfly valve type having adjustable weights on either side thereof to provide a high degree of sensitivity to the existence of a pressure differential on either side of the valve. The present invention is directed to valve construction of this general type.